1. Field of the Invention
Exemplary aspects of the present invention generally relate to a fixing device and an image forming apparatus such as a copier, a facsimile machine, a printer, or a multi-functional system including a combination thereof, and more particularly, to a fixing device using a belt-type fixing member and/or a belt-type pressing member, and an image forming apparatus including the fixing device.
2. Description of the Background Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multi-functional systems having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of an image bearing member; an optical writer projects a light beam onto the charged surface of the image bearing member to form an electrostatic latent image on the image bearing member according to the image data; a developing device supplies toner to the electrostatic latent image formed on the image bearing member to make the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image bearing member onto a recording medium or is indirectly transferred from the image bearing member onto a recording medium via an intermediate transfer member; a cleaning device then cleans the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the unfixed toner image to fix the unfixed toner image on the recording medium, thus forming the image on the recording medium.
The fixing device used in such image forming apparatuses may include an endless belt-shaped fixing member or fixing film formed into a loop, a pressure roller serving as a rotary pressing member disposed opposite the fixing belt loop, a stationary member serving as a pressure support member disposed inside the fixing belt loop, a heater (i.e., a halogen lamp) disposed also inside the fixing belt loop, and so forth.
The stationary member contacts and presses the fixing belt against the pressure roller from the inside of the belt loop, thereby defining a nip between the fixing belt and the pressure roller. The fixing belt is heated by the heater disposed inside the loop. As the recording medium bearing the toner image passes through the nip, heat and pressure are applied to the toner image, thereby fixing the toner image onto the recording medium.
In order to reduce friction between the fixing belt and the stationary member in a known fixing device, typically, a lubricating agent is supplied between the fixing belt and the stationary member, or contact surfaces of both the fixing belt and the stationary member are made of low-friction material. Alternatively, a low-friction slip is provided between the fixing belt and the stationary member.
Although advantageous, the lubricating agent supplied between the fixing belt and the stationary member is exhausted or seeps out over time, resulting in wearing out of the contact surfaces of the fixing belt and the stationary member. In the case of the contact surfaces of the fixing belt and the stationary member made of low-friction material or providing the low-friction slip between the fixing belt and the stationary member, repeated sliding movement over time wears out the contact surfaces of the fixing belt and the stationary member, or the low-friction slip, thereby increasing friction.
An increase in the friction between the fixing belt and the stationary member causes various problems, such as an increase in a drive torque needed for driving these parts, abrasion of the fixing belt and the stationary member, and drifting of the fixing belt which causes image misalignment. These problems are also common in a known fixing device using the stationary member pressing a rotary fixing member through a belt-type pressure member.
In view of the above, there is demand for a device capable of maintaining low friction between a belt member, such as a fixing belt and a pressure belt, and a stationary member slidably contacting the belt member for an extended period of time.